1. Field of the Invention
The invention relates to a compass card for installing whipstocks in subterranean well conduits to effect the installation of the whipstock with the arcuate face of the whipstock disposed at a desired angular relationship with respect to the conduit.
2. Description of the Prior Art
Obstructions and blockages are often encountered in subterranean well casings which interfere with the production or further drilling of the well. In such cases, it has been the practice to deflect the drilling tool angularly so that it cuts through the casing and then produces a new bore which is directed downwardly and laterally in order to pass around the blockage or obstruction and re-orientate the hole. Whenever it is necessary that such hole or window be cut in the casing wall, it is generally required that the angular position of the window be precisely located, so that the new hole will successfully avoid the blockage or other obstructions and will proceed toward the production formation along a prescribed path.
The angular deflection of the drill bit has in the past been accomplished by the installation of a whipstock which is a guide element having a longitudinally tapered arcuate face so as to deflect the drilling tool angularly toward the inside wall of the casing to permit it to cut a hole or window in the casing. Special packers have heretofore been employed for mounting whipstocks in casings, and a common problem of such prior art packers has been the necessity for installing the packer in a precise angular position within the casing in order to insure that the arcuate face of the whipstock will be precisely positioned at the desired angle. For example, U.S. Pat. No. 4,153,109 issued to Szescila discloses a whipstock mounting system wherein the angular orientation of the arcuate face of the whipstock is determined by the engagement of a key slot provided on the whipstock anchor with a key provided in the central bore of a packer. The packer must, therefore, first be located in the well casing with the key in the precise angular position desired to effect the subsequent precise angular location of the arcuate face of the whipstock. This requirement has resulted in the necessity of employing a tubing string to effect the installation of the packer in the well casing resulting in an expensive and time consuming operation.